1. Field of the Invention
The present invention relates to a viewfinder system, and more particularly to a viewfinder system adapted for a single-lens reflex camera in which various kinds of photo-taking information are displayed within the field of view of the viewfinder.
2. Description of Related Art
Heretofore, intra-viewfinder display devices adapted for single-lens reflex cameras and the like have been variously developed. These display devices are arranged to make simultaneously viewable, through a viewfinder optical system, a light measuring range and an automatic focusing distance measuring area arranged on a focusing screen or in a position optically equivalent thereto and various kinds of photo-taking information as well as an object image formed on the focusing screen by a photo-taking lens.
For example, it has been known, as disclosed in Japanese Laid-Open Patent Application No. SHO 55-18664, to dispose, in the neighborhood of a focusing screen, a relief-type hologram in which information obtained by interference of an object wave and a reference wave is converted into surface unevenness and is then recorded, and to provide a display inside a viewfinder by reproducing an image from the hologram. However, it is extremely difficult to form a high quality hologram image on a focusing screen, and the arrangement for the relief-type hologram is expensive as it requires a high level of production technology.
Another known intra-viewfinder display device, as disclosed in Japanese Laid-Open Patent Application No. SHO 58-181034, is arranged to superimpose a liquid crystal display plate on a focusing screen and to provide a display inside the viewfinder by the liquid crystal display plate. According to this arrangement, however, the position of the liquid crystal display in the direction of an optical axis does not exactly coincide with the image forming position on the focusing screen of a photo-taking lens. This positional discrepancy causes some deviation of diopter in viewing through the viewfinder. In addition to that, the liquid crystal member always exists in the optical path of the viewfinder. In the case of a single-lens reflex camera which is required to have a clear, delicate luminous efficiency, the presence of the liquid crystal member in the viewfinder optical path presents a problem as it greatly lowers the quality and quantity of light of a viewfinder image.